US5871665AExpiredUtility
Electrooptical liquid crystal system
Est. expiryApr 27, 2012(expired)· nominal 20-yr term from priority
Inventors:David CoatesOwain Llyr ParriSimon GreenfieldMartin David TillinMark John GouldingPatrick Nolan
C09K 19/14C09K 2323/057C09K 19/2007C09K 2323/00C09K 19/3444C09K 2019/0448C09K 19/38C09K 19/12C09K 19/3469C09K 19/322C09K 2019/0481C09K 19/544
93
PatentIndex Score
65
Cited by
25
References
41
Claims
Abstract
An electrooptical system is disclosed in which a PDLC film is positioned between 2 electrode layers. The PDLC film contains a liquid crystal mixture forming microdroplets in an optically isotropic, transparent polymer matrix. The liquid crystal mixture comprises one or more compounds of formula I ##STR1## wherein R, A 1 , A 2 , Z 1 , Z 2 , X 1 , X 2 , Q, Y and n as herein defined, and one or more reactive liquid crystalline compounds. The PDLC film exhibits improved switching times, especially at low temperatures.
Claims
exact text as granted — not AI-modifiedWe claim:
1. An electrooptical system comprising: two electrode layers between which is contained a PDLC film, said PDLC film comprising a liquid crystal mixture forming microdroplets in an optically isotropic, transparent polymer matrix; wherein said liquid crystal mixture exhibits refractive indices and one of the refractive indices of said liquid crystal mixture is matched to a refractive index of said polymer matrix; wherein said system exhibits an electrically switchable transparency essentially independent of the polarization of the incident light; wherein said PDLC film is made from a precursor and said precursor of said PDLC film comprises said liquid crystal mixture and one or more monomers, oligomers, prepolymers or combination thereof, and a photoinitiator, and is photoradically curable; and said liquid crystal mixture comprises one or more compounds of formula I ##STR85## wherein Z 1 and Z 2 , independently of one another, are each a single bond, --CH 2 CH 2 --, --COO--, --OCO-- or --C.tbd.C--, ##STR86## independently of one another, are each trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of ##STR87## can also be pyrimidine-2,5-diyl, pyridine-2,5-diyl or trans-1,3-dioxane-2,5-diyl, X 1 and X 2 , independently from one another, are each H or F, Q is --CF 2 --, --OCF 2 , --C 2 F 4 --, --OC 2 F 4 -- or a single bond, Y is --H, --F, --Cl or --CN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH 2 groups can also be replaced by --O--, --CH═CH-- or a combination thereof, wherein said liquid crystal mixture further contains one or more reactive liquid crystalline compounds of formula II R'--G'--R" II wherein at least one of the terminal groups R' and R" is a reactive group exhibiting one reaction site selection from HOW' 2 C--, HSW' 2 C--, HW'N--, a carboxyl group, ##STR88## and O═C--N--, or is a polymerizable reactive group exhibiting two or more reactive sites selected from, ##STR89## W' 2 C═CW'--, and ##STR90## wherein W' is in each case independently, H or an alkyl group with 1-5 C atoms, and the other of terminal groups R' and R" is, independently from the first terminal group, one of said reactive groups or is an alkyl radical with up to 15 C atoms which is unsubstituted or mono- or polysubstituted by halogen, it being also possible for one or more CH 2 groups in these radicals to be replaced, in each case independently of one another, by --O--, --S--, --CO--, --OCO--, --CO--O-- or --O--CO--O-- in such a manner that O atoms are not linked directly to one another, G' is a rod-like diyl group of the formula --S.sup.1 --(A.sup.5 --Z.sup.3).sub.m --A.sup.6 --S.sup.2 -- wherein S 1 and S 2 , independently from each other, are alkylene groups with 0-20 C atoms which can be linear or branched, it also being possible for one or more CH 2 groups to be replaced, in each case independently from each other, by --O--, --CO--, --S-- or --NW'-- with the proviso that O atoms are not linked directly to one another, A 5 and A 6 are, independently from each other, a) a cyclohexylene group, wherein one or two non-adjacent CH 2 groups may be replaced by O or S atoms, b) an unsubstituted 1,4-phenylene group wherein one to three CH groups may be replaced by --N-- or a 1,4-phenylene group which is mono- or polysubstituted by F, Cl and/or CH 3 , c) a bicyclo(2,2,2)octylene group, a naphthalene-2,6-diyl group, a decahydronaphthalene-2,6-diyl group or 1,2,3,4-tetrahydronaphthalene group, Z 3 is, independently from each other, --CO--O--, --O--CO--, --CH 2 CH 2 --, --CH 2 O--, --OCH 2 --, --C.tbd.C-- or a single bond, and m is 1, 2, 3 or 4, wherein the amount of said reactive liquid crystalline compounds is not more than 5 wt. % of the mass of the precursor of the PDLC film.
2. An electrooptical system according to claim 1, wherein the amount of said reactive liquid crystalline compound or compounds is 0.01-5 wt. % with respect to the mass of said liquid crystalline mixture.
3. An electrooptical system according to claim 1, wherein said liquid crystal mixture is based on SFM compounds and said system is addressed by an active matrix.
4. An electrooptical system according to claim 1, wherein said liquid crystal mixture is based on carbonitriles and said liquid crystal mixture contains at least 6 compounds.
5. An electrooptical system according to claim 1, wherein said liquid crystal mixture is based on carbonitriles and the ratio of 3- and 4-ring compounds to 2-ring compounds is not less than 0.18.
6. An electrooptical system according to claim 1, wherein said liquid crystal mixture contains at least one reactive liquid crystalline compound exhibiting two reactive groups.
7. An electrooptical system according to claim 1, wherein said liquid crystal mixture contains at least two different reactive liquid crystalline compounds, at least one of which exhibits two reactive groups.
8. An electrooptical system according to claim 2, wherein the amount of said reactive liquid crystalline compound or compounds is less than 2.5 wt. % with respect to the mass of the precursor of said PDLC film.
9. An electrooptical system according to claim 1, wherein said one or more reactive liquid crystalline compounds is one or more compounds of the formula ##STR91## wherein Y 4 is, independently from each other, CH 2 ═CW 4 COO--, CH 2 ═CH-- or HSCH 2 (CH 2 ) m COO--, V 4 is, independently from each other, --O--, --COO--, --OCO--, --S-- or a single bond, W 4 is, independently from each other, H, CH 3 or Cl, m is, independently from each other, 1-7, n is, independently from each other, 1-12, t is 0, 1 or 2, and ##STR92## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene.
10. An electrooptical system according to claim 1, wherein said system contains no polarizers.
11. An electrooptical system according to claim 1, wherein said system contains no orientation layers.
12. An electrooptical system according to claim 1, wherein said system has a thickness of 3-50 μm.
13. An electrooptical system according to claim 12, wherein said system has a thickness of 3-25 μm.
14. An electrooptical system according to claim 1, wherein said system exhibits a switching time τ at 0° C. of 10-47 ms.
15. An electrooptical system according to claim 1, wherein said one or more reactive liquid crystalline compounds exhibits a non-reactive terminal group selected from F, Cl, CF 3 , OCF 3 , OCHF 2 , alkyl or alkoxy.
16. An electrooptical system according to claim 1, wherein said liquid crystalline mixture contains at least one difunctional reactive liquid crystalline compound and at least one monofunctional liquid crystalline compound.
17. An electrooptical system according to claim 1, wherein the amount of said reactive liquid crystalline compounds is 0.1-2 wt. % based on the mass of said precursor of said PDLC film.
18. An electrooptical system according to claim 1, wherein the amount of said reactive liquid crystalline compounds is 0.1-5 wt. % based on the mass of said precursor of said PDLC film.
19. An electrooptical system according to claim 18, wherein the amount of said reactive liquid crystalline compounds is 0.1-2.5 wt. % based on the mass of said precursor of said PDLC film.
20. An electrooptical system according to claim 19, wherein the amount of said reactive liquid crystalline compounds is 0.1-1 wt. % based on the mass of said precursor of said PDLC film.
21. An electrooptical system according to claim 1, wherein Y in formula I is H, F or Cl.
22. An electrooptical system according to claim 1, wherein, in formula I, X 1 is H or F and X 2 is F.
23. An electrooptical system according to claim 1, wherein said system exhibits a switching time τ at 20° C. of 10-31 ms.
24. An electrooptical system comprising: two electrode layers between which is contained in PDLC film, said PDLC film comprising a liquid crystal mixture forming microdroplets in an optically isotropic, transparent polymer matrix, wherein said liquid crystal mixture exhibits refractive indices and one of the refractive indices of said liquid crystal mixture is matched to a refractive index of said polymer matrix; wherein said system exhibits an electrically switchable transparency essentially independent of the polarization of the incident light; wherein said PDLC film is made from a precursor and said precursor of said PDLC film comprises said liquid crystal mixture and one or more monomers, oligomers, prepolymers or combinations thereof, and a photoinitiator, and is photoradically curable; and said liquid crystal mixture comprises one or more compounds of formula I ##STR93## wherein Z 1 and Z 2 , independently of one another, are each a single bond, --CH 2 CH 2 --, --COO--, --OCO-- or --C.tbd.C--, ##STR94## independently of one another, are each trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of ##STR95## can also be pyrimidine-2,5-diyl, pyridine-2,5-diyl or trans-1,3-dioxane-2,5-diyl, X 1 and X 2 m, independently from one another, are each H or F, Q is --CF 2 --, --OCF 2 , --C 2 F 4 --, --OC 2 F 4 -- or a single bond, Y is --H, --F, --Cl or --CN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH 2 groups can also be replaced by --O--, --CH═CH-- or a combination thereof, wherein said liquid crystal mixture further contains one or more reactive liquid crystalline compounds of formula III R.sup.1 --P--X--Z.sup.3 --Z--A.sup.4 --R.sup.2 III wherein R 1 is CH═CW--COO--, ##STR96## ClHN--, (alkyl)HN-- wherein alkyl contains 1-5 C atoms, CH 2 ═CH-- or HS--CH 2 --(CH 2 ) m --COO--; W is H, Cl or alkyl with 1-5 C atoms; m is 1-7; P is alkylene with up to 12 C atoms wherein one or more non-adjacent CH 2 groups can be replaced by --O--; X is --O--, --S--, --COO--, --OCO-- or a single bond; R 2 is an alkyl radical with up to 15 C atoms which is unsubstituted, mono- or polysubstituted by halogen, wherein one or more CH, groups can be replaced, in each case independently of one another, by --O--, --S--, --CO--, --OCO--, --CO--O-- or --O--CO--O-- in such a manner that oxygen atoms are not linked directly to one another, --CN, --Cl or --F, or R 2 has one of the meanings given for R 1 --P--X--; A 3 is 1,4-phenylene or naphthalene-2,6-diyl, in each case being unsubstituted or substituted with 1 to 4 halogen atoms; A 4 is ##STR97## wherein in each case 1,4-phenylene can be substituted by CN or halogen, and one of the 1,4-phenylene groups in (a) or (b) can also be replaced by a 1,4-phenylene radical in which one or two CH groups are replaced by N; and Z is --CO--O--, --O--CO--, --CH 2 CH 2 -- or a single bond, wherein the amount of said reactive liquid crystalline compounds is not more than 5 wt. % of the mass of the precursor of the PDLC film.
25. An electrooptical system according to claim 24, wherein said one or more compounds of formula III is one or more compounds of III1-III20 R.sup.1 --P--X--Phe'--Z--Phe"--R.sup.2 III 1 R.sup.1 --P--X--Phe'--Z--Pyd--Phe"--R.sup.2 III 2 R.sup.1 --P--X--Phe'--Z--Pyr--Phe"--R.sup.2 III 3 R.sup.1 --P--X--Phe'--Z--Phe"--Pyd--R.sup.2 III 4 R.sup.1 --P--X--Phe'--Z--Phe"--Pyr--R.sup.2 III 5 R.sup.1 --P--X--Phe'--Z--Phe"--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 6 R.sup.1 --P--X--Phe'--Z--Pyd--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 7 R.sup.1 --P--X--Phe'--Z--Pyr--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 8 R.sup.1 --P--X--Phe'--Z--Phe"--CH.sub.2 CH.sub.2 --Pyd--R.sup.2III 9 R.sup.1 --P--X--Phe'--Z--Phe"--CH.sub.2 CH.sub.2 --Pyr--R.sup.2III 10 R.sup.1 --P--X--Nap'--Z--Phe"--Phe"--R.sup.2 III 11 R.sup.1 --P--X--Nap'--Z--Pyd--Phe"--R.sup.2 III 12 R.sup.1 --P--X--Nap'--Z--Pyr--Phe"--R.sup.2 III 13 R.sup.1 --P--X--Nap'--Z--Phe"--Pyd--R.sup.2 III 14 R.sup.1 --P--X--Nap'--Z--Phe"--Pyr--R.sup.2 III 15 R.sup.1 --P--X--Nap'--Z--Phe"--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 16 R.sup.1 --P--X--Nap'--Z--Pyd--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 17 R.sup.1 --P--X--Nap'--Z--Pyr--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 18 R.sup.1 --P--X--Nap'--Z--Phe"--CH.sub.2 CH.sub.2 --Pyd--R.sup.2III 19 R.sup.1 --P--X--Nap'--Z--Phe"--CH.sub.2 CH.sub.2 --Pyr--R.sup.2III 20 wherein Phe' is a 1,4-phenylene group ##STR98## X 3-X 6 are, independently from each other, H or halogen; Phe" is a 1,4-phenylene group, which is unsubstituted or mono- or polysubstituted by CN or halogen; Nap' is a naphthalene-2,6-diyl group ##STR99## which is unsubstituted or wherein up to 4 of X 4 -X 12 are independently from each other halogen, while the other denote H; R 1 is CH 2 ═CW--COO--, ##STR100## ClHN--, (alkyl)HN-- wherein alkyl contains 1-5 C atoms, CH 2 ═CH-- or HS--CH 2 --(CH 2 ) m --COO--; W is H, Cl or alkyl with 1-5 C atoms; m is 1-7; R 2 is an alkyl radical with up to 15 C atoms which is unsubstituted, mono- or polysubstituted by halogen, wherein one or more CH 2 groups can be replaced, in each case independently of one another, by --O--, --S--, --CO--, --OCO--, --CO--O-- or --O--CO--O-- in such a manner that oxygen atoms are not linked directly to one another, --CN, --Cl or --F, or R 2 has one of the meanings given for R 1 --P--X--; and Z is --CO--O--, --O--CO--, --CH 2 CH 2 -- or a single bond.
26. An electrooptical system according to claim 24, wherein said one or more compounds according to formula III are of formula ##STR101## wherein Y 1 is, independently from each other, CH 2 ═CW 1 COO--, CH 2 ═CH-- or HS--CH 2 --(CH 2 ) m COO--, V 1 is, independently from each other, --O--, --COO--, --OOC--, --S-- or a single bond, W 1 is independently from each other, H, Cl or CH 3 , n is, independently from each other, 2-12, m is, independently from each other 1-7, and ##STR102## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene.
27. An electrooptical system according to claim 24, wherein said one or more compounds according to formula III are of formula ##STR103## wherein Y 2 is, independently from each other, CH 2 ═CHCOO--, CH 2 ═C(CH 3 )--COO-- or CH 2 ═CH--, V 2 is, independently from each other, --O-- or a single bond, n is, independently from each other 2-12, and ##STR104## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene.
28. An electrooptical system according to claim 24, wherein said one or more compounds according to formula III are of formula ##STR105## wherein Y 3 is, independently from each other, CH 2 ═CW 3 COO--, CH 2 ═CH-- or HSCH 2 (CH 2 ) m --COO--, V 3 is, independently from each other, --O--, --COO--, --OOC--, --S-- or a single bond, W 3 is, independently from each other, H, Cl or CH 3 , a is 0 or 1, n is, independently from each other, 2-12, r is 1 or 2, m is, independently from each other, 1-7 and ##STR106## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene.
29. An electrooptical system according to claim 24, wherein said one or more compounds according to formula III are of formula ##STR107## wherein W 4 is, independently from each other, H, CH 3 or Cl, n is, independently from each other, 1-12, and ##STR108## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene.
30. An electrooptical system according to claim 24, wherein said one or more compounds according to formula III are of formula ##STR109## wherein Y 5 is, independently from each other, CH 2 ═CW 5 COO--, CH 2 ═CH-- or HSCH 2 (CH 2 ) m COO, V 5 is, independently from each other, --O--, --COO--, --OCO--, --S-- or a single bond, W 5 is, independently from each other, H, CH 3 or Cl, n is, independently from each other, 1-12, m is 1-7, t and u are, independently from each other 0, 1, or 2 with the proviso that t+u=1, 2 or 3, and ##STR110## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene.
31. An electrooptical system according to claim 24, wherein said one or more compounds according to formula III are of formula ##STR111## wherein V 5 is, independently from each other, --O--, --COO--, --OCO--, --S-- or a single bond, W 5 is, independently from each other, H, CH 3 or Cl, n is, independently from each other, 1-12, and ##STR112## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene.
32. An electrooptical system comprising: two electrode layers between which is contained a PDLC film, said PDLC film comprising a liquid crystal mixture forming microdroplets in an optically isotropic transparent polymer matrix; wherein said liquid crystal mixture exhibits refractive indices and one of the refractive indices of said liquid crystal mixture is matched to a refractive index of said polymer matrix; wherein said system exhibits an electrically switchable transparency essentially independent of the polarization of the incident light; wherein said PDLC film is made from a precursor and said precursor of said PDLC film comprises said liquid crystal mixture and one or more monomers, oligomers, prepolymers or combinations thereof, and a photoinitiator, and is photoradically curable; and said liquid crystal mixture comprises one or more compounds of formula I ##STR113## wherein Z 1 and Z 2 , independently of one another, are each a single bond, --CH 2 CH 2 --, --COO--, --OCO-- or --C.tbd.C--, ##STR114## independently of one another, are each trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of ##STR115## can also be pyrimidine-2,5-diyl, pyridine-2,5-diyl or trans-1,3-dioxane-2,5-diyl, X 1 and X 2 , independently from one another, are each H or F, Q is --CF 2 --, --OCF 2 , --C 2 F 4 --, --OC 2 F 4 -- or a single bond, Y is --H, --F, --Cl or --CN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH 2 groups can also be replaced by --O--, --CH.tbd.CH-- or a combination thereof, wherein said liquid crystal mixture further contains one or more reactive liquid crystalline compounds of formula ##STR116## wherein Y 7 is CH 2 ═CW 7 COO--, CH 2 ═CH--, HSCH 2 (CH 2 ) m COO--, Y 8 , independently of Y 7 , is Y 7 or an alkyl group with 1-12 C atoms, which is optionally mono- or polysubstituted by F and/or Cl, and/or wherein one or two non-adjacent CH 2 groups may be replaced by --CH═CH--, --O--, --CO--, --COO--, --OCO-- or --S--, V 7 is, independently from each other, --O--, --COO--, --OOC--, --S-- or a single bond, W 7 is, independently from each other, H, Cl or CH 3 , m is, independently from each other 1-7, b is, independently from each other 0-11, and B is ##STR117## with the proviso that in case both Y 7 and Y 8 are CH 2 ═CW 7 COO--, B is ##STR118## wherein the amount of said reactive liquid crystalline compounds is not more than 5 wt. % of the mass of the precursor of the PDLC film.
33. An electrooptical system comprising: two electrode layers between which is contained a PDLC film, said PDLC film comprising a liquid crystal mixture forming microdroplets in an optically isotropic, transparent polymer matrix; wherein said liquid crystal mixture exhibits refractive indices and one of the refractive indices of said liquid crystal mixture is matched to a refractive index of said polymer matrix; wherein said system exhibits an electrically switchable transparency essentially independent of the polarization of the incident light; wherein said PDLC film is made from a precursor and said precursor of said PDLC film comprises said liquid crystal mixture and one or more monomers, oligomers, prepolymers or combinations thereof, and a photoinitiator, and is photoradically curable; and said liquid crystal mixture comprises one or more compounds of formula I ##STR119## wherein Z 1 and Z 2 , independently of one another, are each a single bond, --CH 2 CH 2 --, --COO--, --OCO-- or --C.tbd.C--, ##STR120## independently of one another, are each trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of ##STR121## can also be pyrimidine-2,5-diyl, pyridine-2,5-diyl or trans-1,3-dioxane-2,5-diyl X 1 and X 2 , independently from one another, are each H or F, Q is --CF 2 --, --OCF 2 , --C 2 F 4 --, --OC 2 F 4 -- or a single bond, Y is --H, --F, --Cl, or --CN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH 2 groups can also be replaced by --O--, --CH═CH-- or a combination thereof, wherein said liquid crystal mixture further contains one or more reactive liquid crystalline compounds of formula II R'--G'--R" II wherein one of the terminal groups R' and R" is a reactive group exhibiting one reaction site selected from HOW' 2 C--, HSW' 2 C--, HW'N--, a carboxyl group, ##STR122## and O═C--N--, or is a polymerizable reactive group exhibiting two or more reactive sites selected from ##STR123## W' 2 C═CW'--, and ##STR124## wherein W' is in each case, independently, H or an alkyl group with 1-5 C atoms, and the other of terminal groups R' and R" is, independently from the first terminal group, one of said reactive groups or is an alkyl radical with up to 15 C atoms which is unsubstituted or mono- or polysubstituted by halogen, it being also possible for one or more CH 2 groups in these radicals to be replaced, in each case independently of one another, by --O--, --S--, --CO--, --OCO--, --CO--O-- or --O--CO--O-- in such a manner that O atoms are not linked directly to one another, G' is a rod-like diyl group of the formula --S.sup.1 --(A.sup.5 --Z.sup.3).sub.m --A.sup.6 --S.sup.2 -- wherein S 1 and S 2 , independently from each other, are alkylene groups with 0-20 C atoms which can be linear or branched, it also being possible for one or more CH 2 groups to be replaced, in each case independently from each other, by --O--, --CO--, --S-- or --NW'-- with the proviso that O atoms are not linked directly to one another, A 5 and A 6 are, independently from each other, a) a cyclohexylene group, wherein one or two non-adjacent CH 2 groups may be replaced by O or S atoms, ##STR125## wherein Z 1 and Z 2 , independently of one another, are each a single bond, --CH 2 CH 2 --, --COO--, --OCO-- or --C.tbd.C--, ##STR126## independently of one another, are each trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of ##STR127## can also be pyrimidine-2,5-diyl, pyridine, 2,5-diyl or trans-1,3-dioxane-2,5-diyl, X 1 and X 2 , independently from one another, are each H or F, Q is --CF 2 --, --OCF 2 --, --C 2 F 4 --, --OC 2 F 4 -- or a single bond, Y is --H, --F, --Cl or --CN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH 2 groups can also be replaced by --O--, --CH═CH-- or a combination thereof, wherein said liquid crystal mixture further contains one or more reactive liquid crystalline compounds of formula II R'--G'--R" II wherein one of the terminal groups R' and R" is a reactive group exhibiting one reaction site selected from HOW'C--, HSW' 2 C--, HW'N--, a carboxyl group, ##STR128## and O═C--N-- or is a polymerizable reactive group exhibiting two or more reactive sites selected from ##STR129## W' 2 C═CW'--, and ##STR130## wherein W' is in each case, independently, H or an alkyl group with 1-5 C atoms, and b) an unsubstituted 1,4-phenylene group wherein one to three CH groups may be replaced by --N-- or a 1,4-phenylene group which is mono- or polysubstituted by F, Cl and/or CH 3 , c) a bicyclo(2,2,2)octylene group, a naphthalene-2,6-diyl group, a decahydronaphthalene-2,6-diyl group or 1,2,3,4-tetrahydronaphthalene group, Z 3 is, independently from each other, --CO--O--, --O--CO--, --CH 2 CH 2 --, --CH 2 O--, --OCH 2 --, --C.tbd.C-- or a single bond, and m is 1, 2, 3 or 4; and wherein said reactive liquid crystalline compounds form an internal structure within said microdroplets, and wherein the amount of said reactive liquid crystalline compounds is not more than 5 wt. % of the mass of the precursor of the PDLC film.
34. An electrooptical system according to claim 33, wherein said one or more reactive liquid crystalline compounds is a compound of formula II exhibiting only one reactive group with one reaction site, and said reactive group is coupled to the polymeric matrix with the rest of the molecule being positioned within the microdroplet.
35. An electrooptical system according to claim 33, wherein said liquid crystalline mixture includes a compound of formula II exhibiting two reactive groups R' and R".
36. An electrooptical system according to claim 35, wherein said liquid crystalline mixture include a compound of formula II exhibiting one reactive group R'.
37. An electrooptical system comprising: two electrode layers between which is contained a PDLC film, said PDLC film comprising a liquid crystal mixture forming microdroplets in an optically isotropic, transparent polymer matrix; wherein said liquid crystal mixture exhibits refractive indices and one of the refractive indices of said liquid crystal mixture is matched to a refractive index of said polymer matrix; wherein said system exhibits an electrically switchable transparency essentially independent of the polarization of the incident light; wherein said PDLC film is made from a precursor and said precursor of said PDLC film comprises said liquid crystal mixture and one or more non-liquid crystalline monomers, non-liquid crystalline oligomers, non-liquid crystalline prepolymers or combinations thereof, and a photoinitiator, and is photoradically curable; and said liquid crystal mixture comprises one or more compounds of formula I the other of terminal groups R' and R" is, independently from the first terminal group, one of said reactive groups or is an alkyl radical with up to 15 C atoms which is unsubstituted or mono- or polysubstituted by halogen, it being also possible for one or more CH 2 groups in these radicals to be replaced, in each case independently of one another, by --O--, --S--, --CO--, --OCO--, --CO--O-- or --O--CO--O-- in such a manner that O atoms are not linked directly to one another, G' is a rod-like diyl group of the formula S.sup.1 --(A.sup.5 --Z.sup.3).sub.m --A.sup.6 --S.sup.2 -- wherein S 1 and S 2 , independently from each other, are alkylene groups with 0-20 C atoms which can be linear or branched, it also being possible for one or more CH 2 groups to be replaced, in each case independently from each other, by --O--, --CO--, --S-- or --NW'-- with the proviso that O atoms are not linked directly to one another, A 5 and A 6 are, independently from each other, a) a cyclohexylene group, wherein one or two non-adjacent CH 2 groups may be replaced by O or S atoms, b) an unsubstituted 1,4-phenylene group wherein one to three CH groups may be replaced by --N-- or a 1,4-phenylene group which is mono- or polysubstituted by F, Cl and/or CH 3 , c) a bicyclo(2,2,2)octylene group, a naphthalene-2,6-diyl group, a decahydronaphthalene-2,6-diyl group or 1,2,3,4-tetrahydronaphthalene group, Z 3 is, independently from each other, --CO--O--, --O--CO--, --CH 2 CH 2 --, --CH 2 O--, --OCH 2 --, --C.tbd.C-- or a single bond, and m is 1, 2, 3 or 4, wherein the amount of said reactive liquid crystalline compounds is not more than 5 wt. % of the mass of the precursor of the PDLC film.
38. An electrooptical system comprising: two electrode layers between which is contained a PDLC film, said PDLC film comprising a liquid crystal mixture forming microdroplets in an optically isotropic, transparent polymer matrix; wherein said liquid crystal mixture exhibits refractive indices and one of the refractive indices of said liquid crystal mixture is matched to a refractive index of said polymer matrix; wherein said system exhibits an electrically switchable transparency essentially independent of the polarization of the incident light; wherein said PDLC film is made from a precursor and said precursor of said PDLC film comprises said liquid crystal mixture and one or more monomers, oligomers, prepolymers or combinations thereof, and a photoinitiator, and is photoradically curable; and said liquid crystal mixture comprises one or more compounds of formula I ##STR131## wherein Z 1 and Z 2 , independently of one another, are each a single bond, --CH 2 CH 2 --, --COO--, --OCO-- or --C.tbd.C--, ##STR132## independently of one another, are each trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of ##STR133## can also be pyrimidine-2,5-diyl, pyridine-2,5-diyl or trans-1,3-dioxane-2,5-diyl, X 1 and X 2 , independently from one another, are each H or F, Q is --CF 2 --. --OCF 2 , --C 2 F 4 -- or a single bond, Y is --H, --F, --Cl or --CN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH 2 groups can also be replaced by --O--, --CH═CH-- or a combination thereof, wherein said liquid crystal mixture further contains one or more reactive liquid crystalline compounds of: (a) the formula ##STR134## wherein Y 1 is, independently from each other, CH 2 ═CW 1 COO--, CH 2 ═CH-- or HS--CH 2 --(CH 2 ) m COO--, V 1 is, independently from each other, --O--, --COO--, --OOC--, --S-- or a single bond, W 1 is, independently from each other, H, Cl or CH 3 , n is, independently from each other, 2-12, m is, independently from each other 1-7, and ##STR135## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene; (b) the formula ##STR136## wherein Y 2 is, independently from each other, CH 2 ═CHCOO--, CH 2 ═C(CH 3 )--COO-- or CH 2 ═CH--, V 2 is, independently from each other, --O-- or a single bond, n is, independently from each other 2-12, and ##STR137## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene; (c) the formula ##STR138## wherein Y 3 is, independently from each other, CH 2 ═CW 3 COO--, CH 2 ═CH-- or HSCH 2 (CH 2 ) m --COO--, V 3 is, independently from each other, --O--, --COO--, --OOC--, --S-- or a single bond, W 3 is, independently from each other, H, Cl or CH 3 , a is 0 or 1, n is 1 or 2, m is, independently from each other, 1-7, and ##STR139## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene; (d) the formula ##STR140## wherein Y 4 is, independently from each other, CH 2 ═CW 4 COO--, CH 2 ═CH-- or HSCH 2 (CH 2 ) m COO--, V 4 is, independently from each other, --O--, --COO--, --OCO--, --S-- or a single bond, W 4 is, independently from each other, H, CH 3 or Cl, m is, independently from each other, 1-7, n is, independently from each other, 1-12, t is 0, 1 or 2, and ##STR141## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene; (e) the formula ##STR142## wherein Y 5 is, independently from each other, CH 2 ═CW 5 COO--, CH 2 ═CH-- or HSCH 2 (CH 2 ) m COO, V 5 is, independently from each other, --O--, --COO--, --OCO--, --S-- or a single bond, W 5 is, independently from each other, 1-12, m is 1-7, t and u are, independently from each other 0, 1, or 2 with the proviso that t+u=1, 2 or 3, and ##STR143## is, independently from each other, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,6-difluoro-1,4-phenylene or 2,3,6-trifluoro-1,4-phenylene; or (f) the formula ##STR144## wherein Y 7 is CH 2 ═CW 7 COO--, CH 2 ═CH--, HSCH 2 (CH 2 ) m COO--, Y 8 , independently of Y 7 , is Y 7 or an alkyl group with 1-12 C atoms, which is optionally mono- or polysubstituted by F and/or Cl, and/or wherein one or two non-adjacent CH 2 groups may be replaced by --CH═CH--, --O--, --CO--, --COO--, --OCO-- or --S--, V 7 is, independently from each other, --O--, --COO--, --OOC--, --S-- or a single bond, W 7 is, independently from each other, H, Cl or CH 3 , m is, independently from each other 1-7, b is, independently from each other 0-11, and B is ##STR145## with the proviso that in case both Y 7 and Y 8 are CH 2 ═CW 7 COO--, B is ##STR146## wherein the amount of said reactive liquid crystalline compounds is not more than 5 wt. % of the mass of the precursor of the PDLC film.
39. An electrooptical system comprising: two electrode layers between which is contained a PDLC film, said PDLC film comprising a liquid crystal mixture forming microdroplets in an optically isotropic, transparent polymer matrix; wherein said liquid crystal mixture is based on SFM compounds and exhibits refractive indices and one of the refractive indices of said liquid crystal mixture is matched to a refractive index of said polymer matrix; wherein said system is addressed by an active matrix and exhibits an electrically switchable transparency essentially independent of the polarization of the incident light; wherein said PDLC film is made from a precursor and said precursor of said PDLC film comprises said liquid crystal mixture and one or more monomers, oligomers, prepolymers or combinations thereof, and a photoinitiator, and is photoradically curable; and said liquid crystal mixture comprises one or more compounds of formula I ##STR147## wherein Z 1 and Z 2 , independently of one another, are each a single bond, --CH 2 CH 2 --, --COO--, --OCO-- or --C.tbd.C--, ##STR148## independently of one another, are each trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of ##STR149## can also be pyrimidine-2,5-diyl, pyridine-2,5-diyl or trans-1,3-dioxane-2,5-diyl, X 1 and X 2 , independently from one another, are each H or F, Q is --CF 2 --, --OCF 2 , --C 2 F 4 --, --OC 2 F 4 -- or a single bond, Y is --H, --F, --Cl or --CN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH 2 groups can also be replaced by --O--, --CH═CH-- or a combination thereof, wherein said liquid crystal mixture further contains one or more reactive liquid crystalline compounds of formula II R'--G'--R" II wherein one of the terminal groups R' and R" is a reactive group exhibiting one reaction site selected from HOW' 2 C--, HSW' 2 C--, HW'N--, a carboxyl group, ##STR150## and O═C--N--, or is a polymerizable reactive group exhibiting two or more reactive sites selected from ##STR151## W' 2 C═CW'--, and ##STR152## wherein W' is in each case, independently, H or an alkyl group with 1-5 C atoms, and the other of terminal groups R' and R" is, independently from the first terminal group, one of said reactive groups or is an alkyl radical with up to 15 C atoms which is unsubstituted or mono- or polysubstituted by halogen, it being also possible for one or more CH 2 groups in these radicals to be replaced, in each case independently of one another, by --O--, --S--, --CO--, --OCO--, --CO--O-- or --O--CO--O-- in such a manner that O atoms are not linked directly to one another, G' is a rod-like diyl group of the formula --S.sup.1 --(A.sup.5 --Z.sup.3).sub.m --A.sup.6 --S.sup.2 -- wherein S 1 and S 2 , independently from each other, are alkylene groups with 0-20 C atoms which can be linear or branched, it also being possible for one or more CH 2 groups to be replaced, in each case independently from each other, by --O--, --CO--, --S-- or --NW'-- with the proviso that O atoms are not linked directly to one another, A 5 and A 6 are, independently from each other, a) a cyclohexylene group, wherein one or two non-adjacent CH 2 groups may be replaced by O or S atoms, b) an unsubstituted 1,4-phenylene group wherein one to three CH groups may be replaced by --N-- or a 1,4-phenylene group which is mono- or polysubstituted by F, Cl and/or CH 3 , c) a bicyclo(2,2,2)octylene group, a naphthalene-2,6-diyl group, a decahydronaphthalene-2,6-diyl group or 1,2,3,4-tetrahydronaphthalene group, Z 3 is, independently from each other, --CO--O--, --O--CO--, --CH 2 CH 2 --, --CH 2 O--, --OCH 2 --, --C.tbd.C-- or a single bond, and m is 1, 2, 3 or 4, wherein the amount of said reactive liquid crystalline compounds is not more than 5 wt. % of the mass of the precursor of the PDLC film.
40. An electrooptical system comprising: two electrode layers between which is contained a PDLC film, said PDLC film comprising a liquid crystal mixture forming microdroplets in an optically isotropic, transparent polymer matrix; wherein said liquid crystal mixture exhibits refractive indices and one of the refractive indices of said liquid crystal mixture is matched to a refractive index of said polymer matrix; wherein said system exhibits an electrically switchable transparency essentially independent of the polarization of the incident light; wherein said PDLC film is made from a precursor and said precursor of said PDLC film comprises said liquid crystal mixture and one or more monomers, oligomers, prepolymers or combinations thereof, and a photoinitiator, and is photoradically curable; and said liquid crystal mixture comprises one or more compounds of formula I ##STR153## wherein Z 1 and Z 2 , independently of one another, are each a single bond, --CH 2 CH 2 --, --COO--, --OCO-- or --C.tbd.C--, ##STR154## independently of one another, are each trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of ##STR155## can also be pyrimidine-2,5-diyl, pyridine-2,5-diyl or trans-1,3-dioxane-2,5-diyl, X 1 and X 2 , independently from one another, are each H or F, Q is --CF 2 --, --OCF 2 , --C 2 F 4 --, --OC 2 F 4 -- or a single bond, Y is --H, --F, --Cl or --CN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH 2 groups can also be replaced by --O--, --CH.tbd.CH-- or a combination thereof, wherein said liquid crystal mixture further contains one or more reactive liquid crystalline compounds of formulae III2-III20 R.sup.1 --P--X--Phe'--Z--Pyd--Phe"--R.sup.2 III 2 R.sup.1 --P--X--Phe'--Z--Pyr--Phe"--R.sup.2 III 3 R.sup.1 --P--X--Phe'--Z--Phe"--Pyd--R.sup.2 III 4 R.sup.1 --P--X--Phe'--Z--Phe"--Pyr--R.sup.2 III 5 R.sup.1 --P--X--Phe'--Z--Phe"--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 6 R.sup.1 --P--X--Phe'--Z--Pyd--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 7 R.sup.1 --P--X--Phe'--Z--Pyr--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 8 R.sup.1 --P--X--Phe'--Z--Phe"--CH.sub.2 CH.sub.2 --Pyd--R.sup.2III 9 R.sup.1 --P--X--Phe'--Z--Phe"--CH.sub.2 CH.sub.2 --Pyr--R.sup.2III 10 R.sup.1 --P--X--Nap'--Z--Phe"--Phe"--R.sup.2 III 11 R.sup.1 --P--X--Nap'--Z--Pyd--Phe"--R.sup.2 III 12 R.sup.1 --P--X--Nap'--Z--Pyr--Phe"--R.sup.2 III 13 R.sup.1 --P--X--Nap'--Z--Phe"--Pyd--R.sup.2 III 14 R.sup.1 --P--X--Nap'--Z--Phe"--Pyr--R.sup.2 III 15 R.sup.1 --P--X--Nap'--Z--Phe"--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 16 R.sup.1 --P--X--Nap'--Z--Pyd--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 17 R.sup.1 --P--X--Nap'--Z--Pyr--CH.sub.2 CH.sub.2 --Phe"--R.sup.2III 18 R.sup.1 --P--X--Nap'--Z--Phe"--CH.sub.2 CH.sub.2 --Pyd--R.sup.2III 19 R.sup.1 --P--X--Nap'--Z--Phe"--CH.sub.2 CH.sub.2 --Pyr--R.sup.2III 20 wherein P is alkylene with up to 12 C atoms wherein one or more non-adjacent CH 2 groups can be replaced by --O--; X is --O--, --S--, --COO--, --OCO-- or a single bond; Phe' is a 1,4-phenylene group ##STR156## X 3 -X 6 are, independently from each other, H or halogen; Phe" is a 1,4-phenylene group, which is unsubstituted or mono- or polysubstituted by CN or halogen; Nap' is a naphthalene-2,6-diyl group ##STR157## which is unsubstituted or wherein up to 4 of X 4 -X 12 are independently from each other halogen, while the other denote H; R 1 is CH 2 ═CW--COO--, ##STR158## ClHN--, (alkyl)HN- wherein alkyl contains 1-5 C atoms, CH 2 ═CH-- or HS--CH 2 --(CH 2 ) m --COO--; W is H, Cl or alkyl with 1-5 C atoms; m is 1-7; R 2 is an alkyl radical with up to 15 C atoms which is unsubstituted, mono- or polysubstituted by halogen, wherein one or more CH 2 groups can be replaced, in each case independently of one another, by --O--, --S--, --CO--, --CO--O-- or --O--CO--O-- in such a manner that oxygen atoms are not linked directly to one another, --CN, --Cl or --F, or R 2 has one of the meanings given for R 1 --P--X--; and Z is --CO--O--, --O--CO--, --CH 2 CH 2 -- or a single bond, wherein the amount of said reactive liquid crystalline compounds is not more than 5 wt. % of the mass of the precursor of the PDLC film.
41. An electrooptical system comprising: two electrode layers between which is contained a PDLC film, said PDLC film comprising a liquid crystal mixture forming microdroplets in an optically isotropic, transparent polymer matrix; wherein said liquid crystal mixture exhibits refractive indices and one of the refractive indices of said liquid crystal mixture is matched to a refractive index of said polymer matrix; wherein said system exhibits an electrically switchable transparency essentially independent of the polarization of the incident light; wherein said PDLC film is made from a precursor and said precursor of said PDLC film comprises said liquid crystal mixture and one or more monomers, oligomers, prepolymers or combinations thereof, and a photoinitiator, and is photoradically curable; and said liquid crystal mixture comprises one or more compounds of formula I ##STR159## wherein Z 1 and Z 2 , independently of one another, are each a single bond, --CH 2 CH 2 --, --COO--, --OCO-- or --C.tbd.C--, ##STR160## independently of one another, are each trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene, 2,3-difluoro-1,4-phenylene or 3,5-difluoro-1,4-phenylene, and one of ##STR161## can also be pyrimidine-2,5-diyl, pyridine-2,5-diyl or trans-1,3-dioxane-2,5-diyl. X 1 and X 2 , independently from one another, are each H or F, Q is --CF 2 --, --OCF 2 , --C 2 F 4 --, --OC 2 F 4 -- or a single bond, Y is --H, --F, --Cl or --CN, n is 0, 1 or 2, and R is alkyl having up to 13 C atoms, in which one or two non-adjacent CH 2 groups can also be replaced by --O--, --CH═CH-- or a combination thereof, wherein said liquid crystal mixture further contains 0.1-5 wt. % based on the mass of the precursor of the PDLC film of one or more reactive liquid crystalline compounds of formula II R'--G'--R" II wherein one of the terminal groups R' and R" is a reactive group exhibiting one reaction site selected from HOW' 2 C--, HSW' 2 C--, HW'N--, a carboxyl group, ##STR162## and O═C--N--, or is a polymerizable reactive group exhibiting two or more reactive sites selected from ##STR163## W' 2 C═CW'--, and ##STR164## wherein W' is in each case, independently, H or an alkyl group with 1-5 C atoms, and the other of terminal groups R' and R" is, independently from the first terminal group, one of said reactive groups, or is an alkyl radically with up to 15 C atoms which is unsubstituted or mono- or polysubstituted by halogen, it being also possible for one or more CH 2 groups in these radicals to be replaced, in each case independently of one another, by --O--, --S--, --CO--, --OCO--, --CO--O-- or --O--CO--O-- in such a manner that O atoms are not linked directly to one another, G' is a rod-like diyl group of the formula --S.sup.1 --(A.sup.5 --Z.sup.3).sub.m --A.sup.6 --S.sup.2 -- wherein S 1 and S 2 , independently from each other, are alkylene groups with 0-20 C atoms which can be linear or branched, it also being possible for one or more CH 2 groups to be replaced, in each case independently from each other, by --O--, --CO--, --S-- or --NW'-- with the proviso that O atoms are not linked directly to one another, A 5 and A 6 are, independently from each other, a) a cyclohexylene group, wherein one or two non-adjacent CH 2 groups may be replaced by O or S atoms, b) an unsubstituted 1,4-phenylene group wherein one to three CH groups may be replaced by --N-- or a 1,4-phenylene group which is mono- or polysubstituted by F, Cl and/or CH 3 , c) a bicyclo(2,2,2)octylene group, a naphthalene-2,6-diyl group, a decahydronaphthalene-2,6-diyl group or 1,2,3,4-tetrahydronaphthalene group, Z 3 is independently from each other, --CO--O--, --O--CO--, --CH 2 CH 2 --, --CH 2 O--, --OCH 2 --, --C.tbd.C-- or a single bond, and m is 1, 2, 3 or 4.Cited by (0)
No later patents cite this yet.
References (0)
No backward citations on record.